The collision was reported at 10:28 a.m. at 13th Street and South Van Ness Avenue, fire Capt. Jeanne Seyler said.
The PG&E vehicle was traveling south on South Van Ness Avenue and turned left onto 13th Street where the accident occurred, police spokesman Sgt. Daryl Fong said.
The bicyclist was taken to San Francisco General Hospital to be treated for injuries that are considered life-threatening, Fong said.
PG&E spokesman Joe Molica called the collision "an extremely unfortunate incident" and said the company's "thoughts are with the bicyclist and their family."
The utility, he said, is "strongly committed to safety" and plans to conduct a full investigation and work with local authorities in determining what occurred.
Molica said the utility trains all of its employees on motor vehicle safety.
"We do take it very seriously," he said.